Should we support loading untracked data?

[sfmig]

Is your feature request related to a problem? Please describe.
In PR #201 we discussed if we should support loading untracked data (e.g., manually labelled data, which is often made up of non-consecutive video frames).

It is also closely related to #146.

Describe the solution you'd like
The point of this issue is to discuss if this (or any approximation of this) would be of interest. We could provide functionality to review or clean manual labels. We may want to provide different trackers for people to test on their data too (this would be a very valuable contribution imo).

Describe alternatives you've considered
We could perfectly well focus on dealing with tracked data for now and deal with this in the future.

Additional context
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[sfmig]

On ID tracking tools: this repo may be useful to check https://github.com/TravisWheelerLab/DIPLOMAT/tree/v0.0.2